1. Field of the Invention
The present invention relates to an optically active alcohol having one group or atom selected from silyl group, stannyl group, and halogen atoms at the .gamma.-position and having an epoxy group in the molecule; to a new optically active allyl alcohol having a silyl group at the .gamma.-position; to a precess for producing these optically active alcohols; and to a process for resolving these optically active alcohols having an epoxy group and these optically active allyl alcohols into their respective isomers of high optical purity.
2. Description of the Prior Art
The secondary allyl alcohol is a useful compound per se, and it has been generally regarded as a useful intermediate for synthesis. Recently, a variety of physiologically active compounds containing a skeleton of secondary allyl alcohol in the molecular structure have become well known. These compounds are mostly optically active isomers and the synthesis of optically active isomer of secondary allyl alcohol is a subject of industrial importance.
Where the desired compound to be synthesized is a mixture of complex stereoisomers containing the skeleton of optically active allyl alcohol in the molecular structure, there is a demand for optically active allyl alcohol as an advantageous intermediate that permits various reactions very easily.
For example, in the synthesis of prostaglandin compound, a drug of new type, it is known that an optically active allyl alcohol [IIc] having a halogen atom at the .gamma.-position ##STR7## is converted into an optically active allyl alcohol [IVc] having a halogen atom at the .gamma.-position ##STR8## (where Hal represents a halogen atom; and R represents a saturated or unsaturated, substituted or unsubstituted alkyl group having 1-10 carbon atoms, or a substituted or unsubstituted phenyl group).
The said optically active allyl alcohol [IVc] is used as such as a raw material of the .omega.-side chain. (See J. Org. Chem., 39 2506 (1974), by J. W. Patterson, Jr. et al.)
An optically active allyl alcohol [IVb] having a stannyl group at the .gamma.-position ##STR9## can also be used as a raw material of the .omega.-side chain. (See Tetrahedron Letter, 27, 2199 (1986), by E. J. Coreys, etc.)
A compound of the general formula [VI] below is also reported as a raw material for the .omega.-side chain. ##STR10## (See J. Am. Chem. Soc., 96, 6774 (1974), by J. G. Miller, W. Kurz.)
There are some known processes for the synthesis of optically active secondary allyl alcohol. For example, (1) synthesis by the asymmetric reduction of a conjugated enone [VII]. (See, for example, J. Am. Chem. Soc., 101, 5843 (1979), by Noyori et al.) ##STR11## (2) synthesis by the asymmetrio reduction of a conjugated inone [VIII], followed by hydroamylation and halogenation. (See J. Am. Chem. Soc., 97, 857 (1975), by C. J. Sih et al.) (3) synthesis by the asymmetric reduction of a conjugated inone, followed by hydrogenation. (See J. Am. Chem. Soc., 106, 6717 (1984), by Noyori et al.) ##STR12## These processes, however, are industrially disadvantageous, because they need an expensive enzyme or optically active binaphthol as the asymmetric source, they provide the reaction products [IVb] and [IVc] having an optical purity lower than 97% ee, and they have to be performed with a low substrate concentration at a low reaction temperature (say, -100.degree. C).
On the other hand, Katsuki, Sharpless, et al. showed that a very useful process for synthesizing optically active allyl alcohols is the kinetic optical resolution process. According to this process, titanium tetraalkoxide alcohol and optically active tartaric diester are subjected to the epoxidizing reaction with a peroxide such as t-butyl hydroperoxide. (U.S. Pat. Nos. 4,471,130 and 4,594,439)
The so-called "Sharpless oxidation reaction" is superior to others in that it employs inexpensive tartaric diester as the asymmetric source. In addition, it is now more important than before because of the recent finding that the asymmetric source can be reduced to a catalytic amount. J. Org. Chem., 51, 1922 (1986), by K. B. Sharpless et al.)
Sharpless process, however, still has some problems. First, the kinetic optical resolution of secondary allyl alcohol as disclosed by Sharpless et al. has a disadvantage that there is no satisfactory difference between the epoxidation rate of one specific optically active allyl alcohol and the rate of the other corresponding opposite optically active allyl alcohol. In other words, optically active allyl alcohol of extremely high purity cannot be obtained unless racemic allyl alcohol, a raw material for the epoxidization reaction, is epoxidized more than 60%. (See J. Am. Chem. Soc., 103, 6237 (1981), by K. B. Sharpless et al.)
This means that more than 60% of racemic allyl alcohol, a raw material, is wasted when optically active secondary allyl alcohol of use is to be obtained. This step lowers the yield to less than 40% in the commercial production. After subsequent many complex steps, the final yield of the desired product would be very low.
Secondly, the allyl alcohol disclosed by Sharpless et al. is of less practical use because the cis-isomer is extremely poor in optical resolution.
Thirdly, in the case of allyl alcohol as disclosed by Sharpless et al., there is no example of reaction substrate such as a compound having an electron-withdrawing halogen atom (e.g., a compound [IX] having a bromine atom) and a compound having an easily oxidizable atom (e.g., a compound having a sulfur atom [X] and a compound having a tin atom [Vb]). There is a possibility that the epoxidizing reaction itself does not proceed. Therefore, it could not be an effective kinetic optioal resolution process. ##STR13##
The conceivable reason why the epoxidizing reaction itself does not proceed is that halo-olefins are generally slow in oxidization because the double bond has a low electron density, and that there is a possibility that the oxidation of a tin atom, halogen atom, or sulfur atom is faster than that of olefins.
The other possible reason is that the epoxy alcohol [I] or [II] considered as a reaction product is extremely unstable. ##STR14## The epoxy alcohol is a useful compound per se, and it is also useful as an intermediate for synthesis, because physiologically active compounds containing an optically active epoxy group in the molecular structure have recently been increasing and a compound such as optically active secondary allyl alcohol and optically active 1,2-diol and 1,3-diol which is obtained by the stereospecific reaction at the optically active epoxy group.
However, the optically active epoxy alcohols [I] and [II] having an easily convertible atom such as silicon, tin, and halogen at the .gamma.-position have not been known, and this has been a great hindrance for industrial use.